The 1 in.:1 gal. rule work with fish up to 3 in. After that, a 4 in fish require 5+ gallons, a 6 in. fish requires 10+ gal., and so on. And I was using that "bettas could live in toilets" as a joke. I was just pointing out that bettas are very, very hardy fish. I didn't mean that he could throw bettas in the toilet if he wanted to, God no, I'm just saying that a filter isn't absolutely necessary. Maybe I shoudn't joke around so much. He could just filter about 1/3 water out every week if he wanted to. Most of the fish bowl nation does that with their bettas/goldfish. But I do agree that bettas shouldn't be kept in 8 oz. cups their whole life.
And I apologize, I wasn't implying that you're a newbie, I wouldn't know that. My post just happen to be in the wrong order.